text: 
  from typing import Any, Dict, Optional
  
  if False:
      from zerver.tornado.event_queue import ClientDescriptor
  
  descriptors_by_handler_id = {}  # type: Dict[int, ClientDescriptor]
  
  def get_descriptor_by_handler_id(handler_id: int) -> 'ClientDescriptor':
      return descriptors_by_handler_id.get(handler_id)
  
  def set_descriptor_by_handler_id(handler_id: int,
                                   client_descriptor: 'ClientDescriptor') -> None:
      descriptors_by_handler_id[handler_id] = client_descriptor
  
  def clear_descriptor_by_handler_id(handler_id: int,
                                     client_descriptor: 'ClientDescriptor') -> None:
      del descriptors_by_handler_id[handler_id]
  